With the advantage of high selectivity, moisture stability, thermostability, acid gas resistance, high sorption capacity, and low-cost regenerability, serials of UiO-66(Zr) metal-organic frameworks (MOFs) are considered as promising materials in gas adsorption and purification applications. In this work, we carried out molecular simulations to study the adsorption and membrane separation performance of non-modified UiO-66(Zr) and its functionalized derivatives in sulfur capture from binary sulfur containing gas mixtures. Our results indicate that UiO-66-(COOH)2 and UiO-66-COOH show better adsorption performance in H2S and SO2 capture than other functionalized derivatives. The isosteric heat of adsorption at infinite dilution and radial distribution functions display the existence of strong interactions between hydrophilic functional groups and H2S and SO2. The joint effect of hydrophilism and strong polarity of functional groups promotes the adsorption of H2S and SO2. Both UiO-66-(COOH)2 and UiO-66-COOH are also expected to be ideal membrane candidates for H2S separation because of superior permeation selectivity and permeability.

By using Zeolitic imidazolate framework-67(ZIF-67)/water-ethylene glycol slurry, we separated methane/ethylene gas mixtures by the absorption-adsorption method. The influences of temperature, mass fraction of ZIF-67 in ZIF-67/water-ethylene glycol slurry, pressure, and gas-slurry ratio on the separation performance were studied systematically. We found lower temperature, mass fraction of ZIF-67 of 0.15, higher gas–liquid ratio, and higher operation pressure are suitable for separation of methane/ethylene mixture. The experimental results show by using the slurry we synthesized, the mole fraction of ethylene in gas phase decreases from 74.8 to 53.0%, the selectivity coefficient reaches 10 (much higher than that of solid ZIF-67), and more than 68% of C2H4 can be recovered after one stage of the absorption-adsorption process. Sorption enthalpy of methane and ethylene at low loading is only 11 and 17 kJ/mol, respectively. In addition, the crystal structure of ZIF-67 remains intact after 20 adsorption/desorption cycles.

Molecular dynamics simulations were employed here to explore the molecular mechanism for wetting and spreading behaviors of droplets on smooth and textured substrates in either the absence or presence of surfactants. In particular, we focus on the interplay among substrate hydrophobicity, roughness, and the addition of surfactants. Our simulation results indicate that substrate roughness exerts different effects on the contact angle of nanodroplets, depending on the substrate chemistry, while the presence of surfactants always changes the droplet contact angle via reducing both the vapor–liquid and liquid–solid interfacial tensions, which is independent of the substrate chemistry and roughness. In addition, our calculation results show that the addition of surfactants may lead to the wetting transition of nanodroplets on hydrophobic textured surfaces or induce the appearance of precursor film for droplet spreading on hydrophilic textured surfaces. On the spreading dynamics, we also discuss how the introduction of roughness changes the motion mode of the contact line and how the initial distribution of surfactants affects droplet spreading.

By using a strategy of introducing hydrophobic groups to the linkers, a hydrostable MOF was constructed based on 5-nitroisophthalate and 2,2′-dimethyl-4,4′-bipyridine coligands, revealing a 3D dia topology structure with a 1D channel parallel to the c axis. TGA, PXRD, and water vapor sorption results show high thermal and water stability for the framework. The framework is very porous and possesses not only high busulfan payloads with an encapsulation efficiency up to 21.5% (17.2 wt %) but also very high CO2 selective capture compared with that of other small gases (i.e., CH4, N2, O2, CO, and H2) at 298 K based on molecular simulations due to the pore surface being populated by methyl and nitryl groups. Furthermore, in vitro MTT assays were conducted on four different cells lines with increasing concentrations of the framework, and the results showed that the framework was nontoxic (cell viability >80%) in spite of the concentrations up to 500 μg/mL.

•Water-in-oil (W/O) emulsion was used for the separation of CO2/H2 mixtures.•The synergistic effect of CP and TBAB was used to improve separation ability.•The maximum separation factor of CO2 over H2 reached 103.•H2 could be purified from 53.2 to 97.8 mol% through a two-stage separation.CO2/H2 mixtures, such as integrated gasification combined cycle (IGCC) syngas, were separated via hydrate formation in water-in-oil (W/O) emulsions. The oil phase was composed of diesel and cyclopentane (CP). Span 20 was used to disperse the aqueous phase or hydrate in the oil phase, and tetra-n-butyl ammonium bromide (TBAB) was added to produce a synergistic effect with CP. The experimental results show that the presence of TBAB can remarkably increase the separation ability and improve the flow behavior of the hydrate slurry. The most suitable contents of TBAB in the aqueous phase and water in the emulsion were determined to be 0.29 mol% and 35 vol%, respectively. The maximum separation factor of CO2 over H2 was 103, which is much higher than the literature values for separating CO2/H2 gas mixture via hydrate formation. After a two-stage separation, hydrogen was enriched from 53.2 to 97.8 mol%. The influence of temperature, pressure, and the initial gas–liquid volume ratio on the separation ability and hydrate formation rate were investigated in detail. In addition, a criterion for choosing the suitable operation conditions was suggested based on both phase equilibrium and kinetic factors. Based on this criterion, the suitable operation temperature, pressure, and gas–liquid volume ratio for the separation of CO2/H2 are approximately 270.15 K, 3–5 MPa, and 80–100, respectively.

An absorption–hydration hybrid method was employed for separating C2 components (C2H4 + C2H6) from low-boiling gas mixtures such as refinery dry gas using water-in-diesel emulsions under hydrate formation conditions. Span 20 was used to disperse the water or hydrate in diesel to form the emulsion or hydrate slurry. To simulate a three-stage separation process, three (CH4 + C2H4 + C2H6 + N2) feed gas mixture samples with different gas molar compositions were prepared. Separation experiments were performed under different conditions to investigate the influences of feed composition, temperature, pressure, initial water cut in the emulsion, and initial gas/liquid volume ratio on separation efficiency. The experimental results show that the absorption–hydration hybrid method is obviously superior to the single-absorption method. After three stages of separation at appropriate operating conditions, we found that C2 compounds can be enriched from ∼15 to more than 50 mol % in the (hydrate + diesel) slurry phase and that the content of C2 compounds in the residual gas phase can be reduced to lower than 2 mol %. Low temperature, low initial gas/liquid volume ratio, high pressure, and high water cut were found to be favorable for the recovery of C2 compounds. However, when the temperature was lower than 270.2 K and the water cut was higher than 30 vol %, the formation of flowable hydrate slurry became difficult.

•Recovering ethylene from refinery dry gases using a new absorption–hydration method.•Two-stage separations for CH4 + C2H4 + N2 + H2 gas mixtures were performed.•Separation factor for ethylene increases with decreasing temperature (>269.2 K).•The morphology of water/diesel system was measured by PVM and FBRM probes.•The absorption–hydration method is a promising technology for separating gas mixtures.A so-called absorption–hydration hybrid method was adopted for recovering ethylene from refinery dry gas using water in diesel emulsion under hydrate formation conditions. Span 20 was used to disperse water or hydrate in diesel. Two (CH4 + C2H4 + N2 + H2) quaternary feed gas mixtures were synthesized in order to simulate a two-stage separation of refinery dry gases. The influences of temperature, pressure, feed gas composition, initial gas–liquid volume ratio, and initial water cut in liquid on the separation efficiency were systematically investigated. A pseudo separation factor (S) was defined to evaluate the separation selectivity of ethylene over other components. The experimental results show that ethylene can be enriched in hydrate slurry phase with high selectivity and high recovery ratio. The operation pressure could be reduced remarkably by decreasing temperature to below the ice point. Both separation factor and recovery ratio of ethylene increase with the decrease of temperature; however, when temperature is decreased to 269.2 K or so, the trend changes inversely. In order to reveal why S decreases with decreasing temperature at lower temperature range, in situ PVM (Particle Video Microscope) and FBRM (Focused Beam Reflectance Measurement) particle analyses were performed to investigate the variation law of the morphology of water/diesel dispersion system with temperature before and during hydrate formation. The experimental results show that the average ice particle size increases with decreasing temperature and leads to the decrease of the hydrate formation rate and the conversion ratio of water into hydrate.

In this work a novel method for enhancing the gas storage capacity of metal–organic frameworks (MOFs), i.e. saturating the MOF with a suitable quantity of water and forming hydrates in it, was proposed. Commercialized ZIF-8 was adopted as it is very stable under an atmosphere of water. The adsorption and hydrate formation behaviors of methane in wet ZIF-8 with five different water contents (0.0%, 16.3%, 27.7%, 30.6%, and 35.1%, mass percentages) were investigated under hydrate formation conditions and the storage capacities of both ZIF-8 frameworks and ZIF-8 particle beds were determined. Our results show that hydrates can form in wet ZIF-8 pores and thus increase the overall storage capacities of both ZIF-8 frameworks and ZIF-8 particle beds remarkably. The contribution of hydrates to the total gas uptake of a ZIF-8 framework can be as high as 45%. Compared with dry ZIF-8 frameworks, the net storage capacity of the wet analogue with a water content of 35.1% increases from 5.954 to 9.304 mmol g−1 at 269.15 K and 2.85 MPa, in other words, raised by more than 56%. The ideal volume storage capacity of the wet ZIF-8 framework can achieve more than 190 V/V at 3.0 MPa or so, 7% higher than the DOE target (180 V/V) for methane storage. In addition, our SEM measurements and XRD analysis demonstrate that ZIF-8 is stable during the saturation and hydrate formation processes, illustrating that it can be used repeatedly.

•The inhibition mechanism of some experimental synthesized kinetic hydrate inhibitors (KHIs) was clarified.•The inhibition process of hydrate growth in the absence/presence of KHIs at molecular level was given.•The molecular simulation and experimental studies were combined to testify the inhibition performance of the selected KHIs.Recently, two derivatives of PVP named PVP-A and PVP-E were synthesized by our group and PVP-A was verified to have good inhibition performance by experiments. PVP-A and PVP-E were obtained by introducing a butyl ester group and a butyl ether group into PVP molecules, respectively. In this work, the inhibition process of hydrate growth at molecular level was simulated to explore the inhibition performance of PVP-A, PVP-E, and PVP and clarified their inhibition mechanism. Our simulation results show that PVP-A has the best inhibition performance among these selected KHIs which was in accordance with experiments. The binding interactions between inhibitors and liquid water molecules play a significant role in inhibition performance of KHIs. The strong binding effect could greatly disrupt the hydrogen-bond structure between the water molecules in the vicinity of hydrate nucleus surface and attract more water molecules to form hydrogen bond with KHIs rather than build hydrate clathrate on the surface of hydrate nucleus and therefore prevents the hydrate nucleus reaching the critical nuclear size for subsequent spontaneous growth.

•Recovering ethylene from refinery dry gases using a new absorption–hydration method.•Two-stage separations for CH4 + C2H4 + N2 + H2 gas mixtures were performed.•Separation factor for ethylene increases with decreasing temperature (>269.2 K).•The morphology of water/diesel system was measured by PVM and FBRM probes.•The absorption–hydration method is a promising technology for separating gas mixtures.A so-called absorption–hydration hybrid method was adopted for recovering ethylene from refinery dry gas using water in diesel emulsion under hydrate formation conditions. Span 20 was used to disperse water or hydrate in diesel. Two (CH4 + C2H4 + N2 + H2) quaternary feed gas mixtures were synthesized in order to simulate a two-stage separation of refinery dry gases. The influences of temperature, pressure, feed gas composition, initial gas–liquid volume ratio, and initial water cut in liquid on the separation efficiency were systematically investigated. A pseudo separation factor (S) was defined to evaluate the separation selectivity of ethylene over other components. The experimental results show that ethylene can be enriched in hydrate slurry phase with high selectivity and high recovery ratio. The operation pressure could be reduced remarkably by decreasing temperature to below the ice point. Both separation factor and recovery ratio of ethylene increase with the decrease of temperature; however, when temperature is decreased to 269.2 K or so, the trend changes inversely. In order to reveal why S decreases with decreasing temperature at lower temperature range, in situ PVM (Particle Video Microscope) and FBRM (Focused Beam Reflectance Measurement) particle analyses were performed to investigate the variation law of the morphology of water/diesel dispersion system with temperature before and during hydrate formation. The experimental results show that the average ice particle size increases with decreasing temperature and leads to the decrease of the hydrate formation rate and the conversion ratio of water into hydrate.

In our previous work, we have investigated the adsorption selectivity of CH4/H2 in three pairs of isoreticular metal-organic frameworks (IRMOFs) with and without interpenetration to study the effect of interpenetration on gas mixture separation through Monte Carlo simulation. In addition, the self-diffusivities and the diffusion mechanism of single H2 and CH4 in these MOFs were examined by molecular dynamics simulations. In this work, we extend our previous work to mixed-ligand MOFs to investigate the effects of interpenetration as well as mixed-ligand on both equilibrium-based and kinetic-based gas mixture separation. We found that methane adsorption selectivity is much enhanced in the selected mixed-ligand interpenetrated MOFs compared with their non-interpenetrated counterparts, similar to what we found before for IRMOFs with single-ligand. At room temperature and atmospheric pressure, molecular-level segregation was observed in the mixed-ligand MOFs, and the extent of the effects of interpenetration is comparable for single-ligand and mixed-ligand MOFs. In addition, we found that the diffusion selectivity in the interpenetrated MOFs is similar to the one in their non-interpenetrated counterparts, while the permeation selectivity in the former is much higher than that in the latter, which corroborates our expectation that interpenetration is a good strategy to improve the overall performance of a material as a membrane in separation applications based only on the single component diffusion results. Furthermore, the CH4 permeability of the selected MOF membrane was also evaluated.

In this work, the effect of temperature on adsorption of CO2, CH4, CO, and N2 and separation of their binary mixtures in ZIF-8 were investigated using experimental measurements combining with molecular simulations. The results show that for pure gas adsorption, the effect of temperature is large when strong adsorption occurs, mainly due to the variation of the interaction energy between adsorbate molecules with temperature; while for gas mixtures, systems with large selectivity are more sensitive to temperature. In addition, this work shows that temperature influences the working capacity of CO2 in temperature swing adsorption (TSA) process with the interplay of pressure, which should be considered in the design of TSA process in practical applications.Highlights► A combined experimental and simulation study on effect of temperature on gas adsorption and separation in ZIF-8. ► For pure gases with large isosteric heat of adsorption, the effect of temperature is large. ► For gas mixtures, systems with large selectivity are more sensitive to temperature. ► Temperature influences the working capacity of CO2 with the interplay of pressure.

In this work a novel method for enhancing the gas storage capacity of metal–organic frameworks (MOFs), i.e. saturating the MOF with a suitable quantity of water and forming hydrates in it, was proposed. Commercialized ZIF-8 was adopted as it is very stable under an atmosphere of water. The adsorption and hydrate formation behaviors of methane in wet ZIF-8 with five different water contents (0.0%, 16.3%, 27.7%, 30.6%, and 35.1%, mass percentages) were investigated under hydrate formation conditions and the storage capacities of both ZIF-8 frameworks and ZIF-8 particle beds were determined. Our results show that hydrates can form in wet ZIF-8 pores and thus increase the overall storage capacities of both ZIF-8 frameworks and ZIF-8 particle beds remarkably. The contribution of hydrates to the total gas uptake of a ZIF-8 framework can be as high as 45%. Compared with dry ZIF-8 frameworks, the net storage capacity of the wet analogue with a water content of 35.1% increases from 5.954 to 9.304 mmol g−1 at 269.15 K and 2.85 MPa, in other words, raised by more than 56%. The ideal volume storage capacity of the wet ZIF-8 framework can achieve more than 190 V/V at 3.0 MPa or so, 7% higher than the DOE target (180 V/V) for methane storage. In addition, our SEM measurements and XRD analysis demonstrate that ZIF-8 is stable during the saturation and hydrate formation processes, illustrating that it can be used repeatedly.